The instant invention relates to systems and methods for triggering the deployment or actuation of vehicular safety devices and, more particularly, to a prediction-based system and method which anticipates conditions requiring such deployment or actuation to provide superior response to crash scenarios or "events" of relatively short duration, as might be experienced with a vehicle of frame-chassis construction.
A variety of systems for actuating vehicular safety devices are well known in the art. Such systems are used to sense a crash condition and, in response to such a condition, to actuate an air bag, or lock a seat belt, or actuate a pretensioner for a seat belt retractor. Typically, the safety device is actuated or deployed into its protective position when an impact exceeding a predetermined magnitude is detected by the actuating system.
Alternatively, copending U.S. patent application Ser. No. 07/773,017 teaches a prediction-based system and method for crash discrimination which utilizes a modified velocity term as an event-based timer when predicting future acceleration as the product of a jerk estimate multiplied by event-based time. In this manner, present acceleration information is extrapolated into the future so as to predict when a severe crash is in the making--this, in contrast with other known methods of crash detection, each of which relies upon a certain change in one or more physical quantities (such as estimated vehicle velocity or jerk), perhaps while varying corresponding threshold values over (arbitrary) time to converge to a solution.
In a similar vein, U.S. Pat. No. 5,337,238 teaches a system and method for crash discrimination which features the "damping" of each physical measure upon which crash discrimination, preferably using a damping factor which itself varies as a function of the progress of a crash, i.e., is a function of event-based time. This damping feature effectively provides for the gradual introduction an/or removal of various crash measures from the overall discrimination algorithm.
However, where the crash event is one characterized as having a relatively-short period, as is typical of vehicles having a frame-chassis construction, the modified velocity term used as an event-based timer in U.S. patent application Ser. No. 07/773,017 and in U.S. Pat. No. 5,337,238 will react too slowly, given that a decision as to whether to actuate the safety device must be made in a shorter absolute period of time, based upon a smaller data sample (given the shorter period within which to gather such data). For example, the mid-point of a typical "no-fire" event, i.e., the point of maximal acceleration (deceleration), might be reached after perhaps about forty milliseconds in a frame-chassis vehicle, whereas a like event might produce an acceleration peak after perhaps about sixty or seventy milliseconds in a unibody vehicle. Moreover, since the entire crash pulse is of much shorter duration with a frame-chassis vehicle, and since the amount of energy to be dissipated during the event is the same in both instances (the energy dissipated being equal to the area under the plot of acceleration-versus-time curve), it will be appreciated that the magnitude of acceleration experience by the frame-chassis vehicle is much greater than that of the unibody vehicle.
Accordingly, what is needed is a prediction-based crash discriminator featuring a novel event-based timer with which the crash discriminator can appropriately respond to the shorter-duration crash pulse (with its attendant reduction in the volume of acceleration information available for its use) while managing the higher-magnitude acceleration information generated thereby.